1. Field of the Invention
The present invention relates to an ink jet recording method and an ink jet recording apparatus, and more particularly to an ink jet recording method and an ink jet recording apparatus by which an ink image is formed on an intermediate transfer body having an ink-repellent surface layer and that ink image is transferred to a recording medium to achieve recording.
2. Description of the Related Art
Recording systems for image recording apparatuses in current use for recording and outputting computer-drawn images, copied images from printed matters, facsimile images and the like as required by the user include ink jet, electron-photographic, thermal head and dot impact systems.
Of these systems, the ink jet recording system, by virtue of its relatively simple hardware configuration, has many advantages including a low running cost, the ease of reducing the hardware size and color recording/printing, and adaptability to many different recording medium dimensions from card size to large poster size. Because of these advantages, ink jet recording apparatuses are now attracting keen interest. In particular, ink jet printers, which are available in the market at relatively low prices, are found highly suitable for use with personal computers, digital cameras and so forth. The ink jet recording system is used not only in printers but also in output devices for office automation equipment including facsimile machines and copying machines.
Such an ink jet recording method provides low-noise printing systems, among which the main stream consists of a system whereby which ink is directly ejected onto a material to print as a recording medium, which may be a paper, cloth, plastic sheet or the like, according to image signals to print characters, images and so forth (also known as a direct ejection system). Also, the ink jet recording method, which requires no plate in the printing process, can efficiently print even a small number of copies, and is expected also for industrial use, which requires capability of forming images on a wide variety of recording media. However, the direct ejection system, which constitutes the main stream today, cannot satisfy this requirement. Thus, ink jet recording by the direct discharge system is subject to strict constraints on the choice of the recording medium.
One of its specific constraints is the effect of the ink-absorbency of the recording medium.
The predominant constituent of ink used for ink jet recording is liquid. Therefore, differences in ink-absorbency and permeability of the recording medium affect the reproducibility of the image. Especially a recording medium absorbing no liquid (non-ink-absorbent medium) is subject to a phenomenon in which ink droplets printed adjacently become mixed (bleeding) or another phenomenon of earlier impacting ink droplets being drawn by later impacting ones (beading). Therefore image formation is extremely difficult. Even an ink-permeable recording medium, if its liquid-absorbency (ink-absorbency) is low, would be subject to not only beading and/or bleeding but also a phenomenon known as feathering, in which ink permeates along fibers within the recording medium and accordingly oozes along the fibers, resulting in a poor image. Increasing the ink-absorbency of the recording medium would alleviate these problems, but this could invite penetration of ink (to the rear face of the recording medium).
Many attempts to solve these problems have been proposed by what is known as a transfer system, by which an ink image is temporarily formed on an intermediate transfer body by ink jet recording, the viscosity of that ink image on the intermediate transfer body is increased along with the drying of the ink, or the solvent of the ink image is removed, to concentrate the ink, and then the ink image is transferred from the intermediate transfer body to a recording medium (see U.S. Pat. Nos. 4,438,156 and 5,099,256 and Japanese Patent Application Laid-Open No. 62-92849 (1987)). These proposed methods differ from conventional ink jet recording by which an image is formed by printing directly on a recording medium and causing the moisture of the ink to permeate the recording medium. Therefore, they can be effective against feathering.
Incidentally, not only recording paper specifically intended for ink jet recording use but also plain paper commonly used for electrophotographic copying machines is often used as the recording medium for the formation of color images by ink jet recording. Plain paper is produced by many manufacturers, and the quality and hue of even white paper subtly differ from one manufacturer to another. Moreover, recycled paper is in expanding use today, a circumstance that contributes to further increasing hue differences among recording media. In addition, ink jet recording on a wide variety of recording media, including those on which a color and/or a pattern are printed in advance and those having transparent base, has come to be required.
An image formed on one of these diverse recording media is considerably influenced by the color and pattern of that particular recording medium. In view of this problem, it is proposed to use white ink for recording on any non-white recording medium (see Japanese Patent Application Laid-Open No. 2001-253065). More specifically, Japanese Patent Application Laid-Open No. 2001-253065 discloses a technique by which inks of a plurality of colors including white are made ready for use, the level of whiteness of the recording medium is determined, and white ink in addition to color inks (cyan, magenta, yellow and black) is used for image formation on a medium whose level of whiteness is below a specified level (i.e. a non-white medium).
However, the system disclosed by this Japanese Patent Application Laid-Open No. 2001-253065 uses no intermediate transfer body but directly applies color inks for image formation to a recording medium. Therefore it is unsuitable for recording media which are poor in ink absorbency as discussed above. If the method of Japanese Patent Application Laid-Open No. 2001-253065 is applied to, for instance, a low ink-absorbency recording medium, the white ink and color inks will become mixed on the recording medium, and the white portion, which should be an undercoat, will be distorted, hardly serving as an undercoat.
Considering these factors, it is desirable to work out an image formation system that permits white undercoating while using an intermediate transfer body. Such an image formation system is realized by a technique disclosed in Japanese Patent Application Laid-Open No. 2003-25554.
According to this Japanese Patent Application Laid-Open No. 2003-25554, high molecular granules which can be dissolved in, or inflated by the moisture of, ink are formed in advanced on an intermediate transfer body, and droplets of color inks (cyan, magenta, yellow and black) are jetted from an ink jet recording head onto the intermediate transfer body on which the granules are formed to generate a visible image. After forming along with that a white background is formed by jetting white ink onto the non-image portion where this visible image is not generated, the image and the white background are transferred to the recording medium.
However, the technique according to Japanese Patent Application Laid-Open No. 2003-25554, as no white ink is applied to the portion where no visible image is formed, involves a problem that the influences of the color and pattern of the recording medium in the undercoat portion for the visible image cannot be sufficiently alleviated.
As is evident from the foregoing description, no proposal has been made as yet of a technique by which, while making it possible to form an image on a low ink-absorbency recording medium, the influences of the color and pattern of the recording medium in the undercoat portion for the formed image can be sufficiently alleviated. As a consequence, the advantages of the ink jet recording system including printing ease and adaptability to small number of copies printing are not yet fully utilized in industrial applications.